Method and apparatus for cleaning and surface conditioning objects using plasma

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation-in-part of U.S. patent application Ser. No. 11/143,083, filed Jun. 2, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/143,552, filed Jun. 2, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/043,787, filed Jan. 26, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/040,222, filed Jan. 21, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 11/039,628, filed Jan. 20, 2005, which is a divisional of U.S. patent application Ser. No. 10/858,272, filed Jun. 1, 2004, which application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/478,418, filed on Jun. 16, 2003, all prior applications of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003Embodiments of the present invention generally relate to a method and apparatus for cleaning and surface conditioning fluid handling devices and in particular to a method and apparatus for cleaning and surface conditioning portions of fluid handling devices using plasma.

00042. Description of the Related Art

0005In certain clinical, industrial and life science testing laboratories, extremely small quantities of fluids, for example, volumes between a drop (about 25 microliters) and a few nano-liters may need to be analyzed. Several known methods are employed to transfer these small amounts of liquid compounds from a source to a testing device. Generally, liquid is aspirated from a fluid holding device into a fluid handling device. The fluid handling device may include, but is not limited to, a probe, cannula, disposable pipette, pin tool or other similar component or plurality of such components (hereinafter collectively referred to as “probes”). The fluid handling device and its probes may move, manually, automatically or robotically, dispensing the aspirated liquid into another fluid holding device for testing purposes.

0006Commonly, the probes, unless disposable, are reused from one test to the next. As a result, at least the tips of the probes must be cleaned between each test. Conventionally, the probes undergo a wet “tip wash” process. That is, they are cleaned in between uses with a liquid solvent, such as Dimethyl Sulfoxide (DMSO) or simply water.

0007These methods and apparatus for cleaning and conditioning fluid handling devices have certain disadvantages. For example, the wet “tip wash” process takes a relatively long time and can be ineffective in cleaning the probe tips to suitable levels of cleanliness. Furthermore, disposing the used solvents from the wet process presents a challenge. Thus, there is a need for improved methods and apparatus for cleaning and surface conditioning fluid handling devices.

SUMMARY OF THE INVENTION

0008The present invention generally relates to an apparatus and method for cleaning at least a portion of a fluid handling device, which device includes a plurality of probes, using plasma.

0009In one embodiment of the present invention, there is provided an apparatus for cleaning objects using plasma, comprising a plurality of elongated dielectric barrier members arranged adjacent each other; a plurality of electrodes, each contained within, and extending substantially along the length of, respective ones of the elongated dielectric barrier members; and a ground plane proximate the plurality of elongated dielectric barrier members.

0010In accordance with another embodiment of the present invention, there is provided an apparatus for cleaning objects using plasma, comprising a plurality of elongated dielectric barrier members arranged adjacent each other in a microtiter plate matrix format; a plurality of electrodes, each contained within, and extending substantially along the length of, respective ones of the elongated dielectric barrier members; and a ground plane proximate the plurality of elongated dielectric barrier members.

0011In accordance with yet another embodiment of the present invention, there is provided a method for cleaning at least a portion of a plurality of probes, comprising providing a plurality of elongated dielectric barrier members having electrodes arranged therein; providing a ground plane proximate the plurality of elongated dielectric barrier members; introducing the probes proximate the elongated dielectric barrier members and ground plane; and generating a dielectric barrier discharge to form plasma between the elongated dielectric barrier members and ground plane for cleaning at least a portion of each of the probes.

BRIEF DESCRIPTION OF THE DRAWINGS

0012So the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the present invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted; however, the appended drawings illustrate only typical embodiments of the present invention and are therefore not to be considered limiting of its scope, for the present invention may admit to other equally effective embodiments.

0013<figref idref="DRAWINGS">FIG. 1A</figref> is a top, partial perspective view of a plurality of conductive probes being introduced to a plurality of elongated dielectric barrier members with coupled inner electrodes in accordance with an embodiment of the present invention;

0014<figref idref="DRAWINGS">FIG. 1B</figref> is a top, partial perspective view of one conductive probe being introduced to one dielectric barrier member with a coupled inner electrode in accordance with an embodiment of the present invention;

0015<figref idref="DRAWINGS">FIG. 2</figref> is a front, expanded view of the device and the conductive probes of <figref idref="DRAWINGS">FIG. 1A</figref> showing the components electrically coupled;

0016<figref idref="DRAWINGS">FIG. 3A</figref> is a cross sectional schematic view of the device and a conductive probe of <figref idref="DRAWINGS">FIG. 1A</figref> showing the dimensions and spacing among components;

0017<figref idref="DRAWINGS">FIG. 3B</figref> is a cross sectional schematic view of the device of <figref idref="DRAWINGS">FIG. 1A</figref> showing a conductive probe proximate the top of a dielectric barrier member;

0018<figref idref="DRAWINGS">FIG. 4</figref> is a top plan view of a matrix or array of the device of <figref idref="DRAWINGS">FIG. 1A</figref> showing the plurality of elongated dielectric barrier members arranged in a microtiter plate format;

0019<figref idref="DRAWINGS">FIG. 5</figref> represents a graph of the relative concentrations of different chemical and particle species of plasma in time after the initiation of a single microdischarge that forms atmospheric pressure plasma in air;

0020<figref idref="DRAWINGS">FIG. 6</figref> is a top, partial perspective view of a plurality of probes being introduced to a plurality of elongated dielectric barrier members with coupled inner electrodes in accordance with another embodiment of the present invention;

0021<figref idref="DRAWINGS">FIG. 7</figref> is a top, partial perspective view of a plurality of probes being introduced to a plurality of elongated dielectric barrier members with coupled inner electrodes in accordance with yet another embodiment of the present invention;

0022<figref idref="DRAWINGS">FIG. 8</figref> is a partial, cross sectional view of the embodiment shown in <figref idref="DRAWINGS">FIG. 7</figref>; and

0023<figref idref="DRAWINGS">FIG. 9</figref> is a top plan view of a matrix or array of the devices of <figref idref="DRAWINGS">FIG. 6</figref> or <b>7</b> showing the plurality of elongated dielectric barrier members arranged in a microtiter plate format.

0024While embodiments of the present invention are described herein by way of example using several illustrative drawings, those skilled in the art will recognize the present invention is not limited to the embodiments or drawings described. It should be understood the drawings and the detailed description thereto are not intended to limit the present invention to the particular form disclosed, but to the contrary, the present invention is to cover all modification, equivalents and alternatives falling within the spirit and scope of embodiments of the present invention as defined by the appended claims.

0025The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “can” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures.

DETAILED DESCRIPTION

0026The term “plasma” is used to describe a quasi-neutral gas of charged and neutral species characterized by a collective behavior governed by coulomb interactions. Plasma is typically obtained when sufficient energy, higher than the ionization energy of the neutral species, is added to the gas causing ionization and the production of ions and electrons. The energy can be in the form of an externally applied electromagnetic field, electrostatic field, or heat. The plasma becomes an electrically conducting medium in which there are roughly equal numbers of positively and negatively charged particles, produced when the atoms/molecules in a gas become ionized.

0027A plasma discharge is produced when an electric field of sufficient intensity is applied to a volume of gas. Free electrons are then subsequently accelerated to sufficient energies to produce electron-ion pairs through inelastic collisions. As the density of electrons increase, further inelastic electron atom/molecule collisions will result in the production of further charge carriers and a variety of other species. The species may include excited and metastable states of atoms and molecules, photons, free radicals, molecular fragments, and monomers.

0028The term “metastable” describes a type of atom/molecule excited to an upper electronic quantum level in which quantum mechanical selection rules forbid a spontaneous transition to a lower level. As a result, such species have long, excited lifetimes. For example, whereas excited states with quantum mechanically allowed transitions typically have lifetimes on the order of 10⁻⁹to 10⁻⁸seconds before relaxing and emitting a photon, metastable states can exist for about 10⁻⁶to 10¹seconds. The long metastable lifetimes allow for a higher probability of the excited species to transfer their energies directly through a collision with another compound and result in ionization and/or dissociative processes.

0029The plasma species are chemically active and/or can physically modify the surface of materials and may therefore serve to form new chemical compounds and/or modify existing compounds. For example, the plasma species can modify existing compounds through ionization, dissociation, oxidation, reduction, attachment, and recombination.

0030A non-thermal, or non-equilibrium, plasma is one in which the temperature of the plasma electrons is higher than the temperature of the ionic and neutral species. Within atmospheric pressure non-thermal plasma, there is typically an abundance of the aforementioned energetic and reactive particles (i.e., species), such as ultraviolet photons, excited and/or metastable atoms and molecules, atomic and molecular ions, and free radicals. For example, within an air plasma, there are excited, metastable, and ionic species of N₂, N, O₂, O, free radicals such as OH, HO₂, NO, O, and O₃, and ultraviolet photons ranging in wavelengths from 200 to 400 nanometers resulting from N₂, NO, and OH emissions. In addition to the energetic (fast) plasma electrons, embodiments of the present invention harness and use these “other” particles to clean and surface condition portions of liquid handling devices, such as probes, and the like.

0031Referring to <figref idref="DRAWINGS">FIG. 1A</figref>, a partial view of a non-thermal atmospheric pressure plasma cleaning device <b>100</b> in accordance with an embodiment of the present invention is disclosed. The device <b>100</b> includes a plurality of elongated dielectric barrier members <b>102</b> arranged in a matrix or array, which lie in a plane. The members <b>102</b> are substantially regularly spaced apart from each other forming a gap <b>103</b> between adjacent members <b>102</b>. Each dielectric barrier member <b>102</b> includes an inner electrode <b>104</b> extending within, and substantially along the length of, respective elongated dielectric barrier members <b>102</b>. A plurality of conductive probes <b>106</b> are shown extending into open spaces or gaps <b>103</b> between the plurality of dielectric barrier members <b>102</b>. In one embodiment, the probes <b>106</b> are part of a fluid handling device. As such, the probes <b>106</b> are attached to and extend from a fluid handling device (not shown), which may be part of a microtiter plate test bed set up. In other embodiments, the probes <b>106</b> may be any form of a conductive element that would benefit from plasma cleaning.

0032The elongated dielectric barrier members <b>102</b> are made of any type of material capable of providing a surface for a dielectric barrier discharge of atmospheric pressure plasma (described herein). Dielectric barrier material useful in this embodiment of the present invention includes, but is not limited to, ceramic, glass, plastic, polymer epoxy, or a composite of one or more such materials, such as fiberglass or a ceramic filled resin (available from Cotronics Corp., Wetherill Park, Australia).

0033In one embodiment, a ceramic dielectric barrier is alumina or aluminum nitride. In another embodiment, a ceramic dielectric barrier is a machinable glass ceramic (available from Corning Incorporated, Corning, N.Y.). In yet another embodiment of the present invention, a glass dielectric barrier is a borosilicate glass (also available from Corning Incorporated, Corning, N.Y.). In still another embodiment, a glass dielectric barrier is quartz (available from GE Quartz, Inc., Willoughby, Ohio). In an embodiment of the present invention, a plastic dielectric barrier is polymethyl methacrylate (PLEXIGLASS and LUCITE, available from Dupont, Inc., Wilmington, Del.). In yet another embodiment of the present invention, a plastic dielectric barrier is polycarbonate (also available from Dupont, Inc., Wilmington, Del.). In yet another embodiment, a plastic dielectric barrier is a fluoropolymer (available from Dupont, Inc., Wilmington, Del.). In another embodiment, a plastic dielectric barrier is a polyimide film (KAPTON, available from Dupont, Inc., Wilmington, Del.). Dielectric barrier materials useful in the present invention typically have dielectric constants ranging between 2 and 30. For example, in one embodiment that uses a polyimide film plastic such as KAPTON, at 50% relative humidity, with a dielectric strength of 7700 Volts/mil, the film would have a dielectric constant of about 3.5.

0034The inner electrode <b>104</b> may comprise any conductive material, including metals, alloys and conductive compounds. In one embodiment, a metal may be used. Metals useful in this embodiment of the present invention include, but are not limited to, copper, silver, aluminum, and combinations thereof. In another embodiment of the present invention, an alloy of metals may be used as the inner electrode <b>104</b>. Alloys useful in this embodiment of the present invention include, but are not limited to, stainless steel, brass, and bronze. In another embodiment of the present invention, a conductive compound may be used. Conductive compounds useful in the present invention include, but are not limited to, indium-tin-oxide.

0035The inner electrodes <b>104</b> of the present invention may be formed using any method known in the art. For example, in one embodiment of the present invention, the inner electrodes <b>104</b> may be formed using a foil. In another embodiment of the present invention, the inner electrodes <b>104</b> may be formed using a wire. In yet another embodiment of the present invention, the inner electrodes <b>104</b> may be formed using a solid block of conductive material. In another embodiment of the present invention, the inner electrodes <b>104</b> may be deposited as an integral layer directly onto the inner core of the dielectric barrier members <b>102</b>. In one such embodiment, an inner electrode <b>104</b> may be formed using a conductive paint, which is applied to the inner core of the elongated dielectric barrier members <b>102</b>. Alternative electrode designs are contemplated by embodiments of the present invention.

0036In one use of the present invention, the conductive probes <b>106</b> are part of the fluid handling device and are introduced in the gap <b>103</b>, i.e., proximate the elongated dielectric barrier members <b>102</b> of the plasma cleaning device <b>100</b>. Use of the term “probe” throughout this application is meant to include, but not be limited to, probes, cannulas, pin tools, pipettes and spray heads or any portion of a fluid handling device that is capable of carrying fluid. These portions can be generally hollow to carry the fluid but may be solid and include a surface area capable of retaining fluid. All of these different types of fluid handling portions of a fluid handling device are collectively referred to in this application as “probes.” In an embodiment, the probe is conductive and is made of conductive material similar to that material described above in connection with the inner electrode <b>104</b>. In other embodiments, as described below, the probe is non-conductive.

0037<figref idref="DRAWINGS">FIG. 1B</figref> depicts a non-thermal atmospheric pressure plasma cleaning device <b>100</b>′ in accordance with another embodiment of the present invention. In this embodiment, only one elongated dielectric barrier member <b>102</b>′ and one inner electrode <b>104</b>′ are shown. In addition, only one conductive probe <b>106</b>′ is introduced proximate the dielectric <b>102</b>′. However, multiple elongated dielectric barrier members <b>102</b>′ with respective inner electrodes <b>104</b>′, where conductive probes <b>106</b>′ are introduced proximate the elongated dielectric barrier members <b>102</b>′ are contemplated by embodiments of the present invention.

0038Each conductive probe <b>106</b> may be introduced proximate one (<figref idref="DRAWINGS">FIG. 1B</figref>) or more (<figref idref="DRAWINGS">FIG. 1A</figref>) elongated dielectric barrier members <b>102</b>. When each conductive probe <b>106</b> is proximate one elongated dielectric barrier member <b>102</b>, the conductive probe <b>106</b> may be introduced proximate the top of the elongated dielectric barrier member <b>102</b> as best shown in <figref idref="DRAWINGS">FIG. 1B</figref>. When each conductive probe <b>106</b> is introduced proximate two elongated dielectric barrier members <b>102</b>, the conductive probe <b>106</b> may be introduced proximate or between the two elongated dielectric barrier members <b>102</b>, as best shown in <figref idref="DRAWINGS">FIG. 1A</figref>.

0039Referring to <figref idref="DRAWINGS">FIG. 2</figref>, a portion of an atmospheric pressure plasma device is designated <b>200</b>. This section <b>200</b> includes a plurality of inner electrodes <b>204</b> of each respective elongated dielectric barrier member <b>202</b> electrically connected to an AC voltage source <b>208</b>. The conductive probes <b>206</b> are electrically grounded with respect to the AC voltage source <b>208</b>. The AC voltage source <b>208</b> in this embodiment includes an AC source <b>207</b>, a power amplifier <b>209</b> and a transformer <b>211</b> to supply voltage to the inner electrodes <b>204</b>.

0040In certain embodiments of the atmospheric pressure plasma device <b>200</b>, a dielectric barrier discharge (DBD) (also known as a “silent discharge”) technique is used to create microdischarges of atmospheric pressure plasma. In a DBD technique, a sinusoidal voltage from an AC source <b>207</b> is applied to at least one inner electrode <b>204</b>, within an insulating dielectric barrier member <b>202</b>. Dielectric barrier discharge techniques have been described in “Dielectric-barrier Discharges: Their History, Discharge Physics, and Industrial Applications”, Plasma Chemistry and Plasma Processing, Vol. 23, No. 1, March 2003, and “Filamentary, Patterned, and Diffuse Barrier Discharges”, IEEE Transactions on Plasma Science, Vol. 30, No. 4, Aug. 2002, both authored by U. Kogelschatz, the entire disclosures of which are incorporated by reference herein.

0041In short, to obtain a substantially uniform atmospheric pressure plasma in air, a dielectric barrier is placed in between the electrode <b>204</b> and the conductive probe <b>206</b> to control the discharge, i.e., choke the production of atmospheric pressure plasma. That is, before the discharge can become an arc, the dielectric barrier <b>202</b> chokes the production of the discharge. Because this embodiment is operated using an AC voltage source, the discharge oscillates in a sinusoidal cycle. The microdischarges occur near the peak of each sinusoid. One advantage to this embodiment is that controlled non-equilibrium plasmas can be generated at atmospheric pressure using a relatively simple and efficient technique.

0042In operation, the AC voltage source <b>208</b> applies a sinusoidal voltage to the inner electrodes <b>204</b>. Then, the plurality of conductive probes <b>206</b> are introduced into the gap <b>203</b> between adjacent elongated dielectric barriers <b>202</b>. A dielectric barrier discharge (DBD) is produced. This DBD forms atmospheric pressure plasma, represented by arrows <b>210</b>. In an embodiment of the present invention, atmospheric pressure plasma is obtained when, during one phase of the applied AC voltage, charges accumulate between the dielectric surface and the opposing electrode until the electric field is sufficiently high enough to initiate an electrical discharge through the gas gap (also known as “gas breakdown”).

0043During an electrical discharge, an electric field from the redistributed charge densities may oppose the applied electric field and the discharge is terminated. In one embodiment, the applied voltage-discharge termination process may be repeated at a higher voltage portion of the same phase of the applied AC voltage or during the next phase of the applied AC voltage. A point discharge generally develops within a high electric field region near the tip of the conductive probe <b>206</b>.

0044To create the necessary DBD for an embodiment of the present invention, the AC voltage source <b>208</b> includes an AC power amplifier <b>209</b> and a high voltage transformer <b>211</b>. The frequency ranges from about 10,000 Hertz to about 20,000 Hertz, sinusoidal. The power amplifier has an output voltage of from about 0 Volts (rms) to about 22.5 Volts (rms) with an output power of about 500 watts. The high voltage transformer ranges from about 0 V (rms) to 7,000 Volts (rms) (which is about 10,000 volts (peak)). Depending on the geometry and gas used for the plasma device, the applied voltages can range from about 500 to about 10,000 Volts (peak), with frequencies ranging from line frequencies of about 50 Hertz up to about 20 Megahertz.

0045In an embodiment of the present invention, the frequency of a power source may range from 50 Hertz up to about 20 Megahertz. In another embodiment of the present invention, the voltage and frequency may range from about 5,000 to about 15,000 Volts (peak) and about 50 Hertz to about 50,000 Hertz, respectively.

0046The gas used in the plasma device <b>200</b> embodiment of the present invention can be ambient air, pure oxygen, any one of the rare gases, or a combination of each such as a mixture of air or oxygen with argon and/or helium. Also, the gas may include an additive, such as hydrogen peroxide, or organic compounds such as methanol, ethanol, ethylene or isopropynol to enhance specific atmospheric pressure plasma cleaning properties.

0047<figref idref="DRAWINGS">FIG. 3A</figref> depicts one example of the geometry and relationship among components of one embodiment of the present invention. The elongated dielectric barrier member <b>302</b> may comprise, for example, an elongated hollow tube with a hollow inner electrode <b>304</b> extended substantially the length of the elongated dielectric barrier member <b>302</b>. Alternatively, the elongated dielectric barrier member <b>302</b> may be other than a tube such as a solid with a solid inner electrode <b>304</b>. The elongated dielectric barrier <b>302</b> may be formed of different shapes as well. For example, and not in any way limiting, the shape of the elongated dielectric barrier may be tubular, circular, square, rectangular, oval, polygonal, triangular, trapezoidal, rhombus and irregular. If tubular, each dielectric barrier tube is about 2 mm in diameter and about 75 to about 120 mm long.

0048The elongated dielectric barrier members <b>302</b> are placed adjacent one another, defining a plane. They are spaced at regular intervals and form a gap <b>303</b>, designated as spacing A. Alternatively, the members <b>302</b> can be staggered in a non-planar arrangement with respect to one another. The spacing A is sized to allow at least a portion of each of the plurality of probes to be introduced proximate or between the elongated dielectric barrier members. The gap <b>303</b> or spacing A can approach zero, provided there is a sufficient gap to allow gas such as air to flow through the elongated dielectric barrier members <b>302</b>. Spacing A or gap <b>303</b> can range from about 0 mm to about 10 mm. The spacing A or gap <b>303</b> may also range from about 2 mm to about 9.5 mm. In one embodiment, the spacing A is about 9 mm. In another embodiment, the spacing A is about 4.5 mm. In yet another embodiment, the spacing A is about 2.25 mm.

0049In an embodiment, where both the probes <b>306</b> and the plurality of elongated dielectric barrier members <b>302</b> are substantially tubular (each having substantially the same respective diameter) and the plurality of probes <b>306</b> are substantially tubular (each having substantially the same respective diameter), the probe <b>306</b> diameter is relatively smaller than the diameter of the plurality of elongated dielectric barrier members. Thus, even if the spacing A (or gap <b>303</b>) between the elongated dielectric barrier members <b>302</b> approaches 0 mm, the probes <b>306</b> can be introduced proximate, if not between, a pair of elongated dielectric members <b>302</b>.

0050Alternatively, as shown in <figref idref="DRAWINGS">FIG. 3B</figref>, the probes <b>306</b>′ can be introduced generally proximate the top of each elongated dielectric barrier member <b>302</b>′. <figref idref="DRAWINGS">FIG. 3B</figref> depicts only one probe <b>306</b>′ and one dielectric <b>302</b>′ but it is to be understood the present invention contemplates a plurality of probes <b>306</b>′ being introduced proximate the top of respective dielectric barrier members <b>302</b>′.

0051Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a top plan view of the above described plasma device configured and arranged in a standard microtiter plate format <b>400</b>. For example, the microtiter plate format may be sized to accommodate about 96 openings for receiving a plurality of fluid handling probes. Alternatively, the microtiter plate is sized to accommodate about 384 openings for receiving a plurality of probes as depicted in <figref idref="DRAWINGS">FIG. 4</figref>. As an alternative, the wells and the pitch between rows of wells of the microtiter plate are sized to accommodate about 1536 openings for receiving a plurality of probes.

0052Microtiter plates or microplates, similar to the one depicted in <figref idref="DRAWINGS">FIG. 4</figref>, are small, usually plastic, reaction vessels. The microplate <b>400</b> has a tray or cassette <b>410</b> covered with wells or dimples <b>412</b> arranged in orderly rows. These wells <b>412</b> are used to conduct separate chemical reactions during a fluid testing step. The large number of wells, which typically number 96, 384 (as shown in <figref idref="DRAWINGS">FIG. 4</figref>) or 1536, depending upon the well size and pitch between rows of wells of the microplate allow for many different reactions to take place at the same time. Microplates are ideal for high-throughput screening and research. They allow miniaturization of assays and are suitable for many applications including drug testing, genetic study, and combinatorial chemistry.

0053The microplate <b>400</b> has been equipped with an embodiment of the present invention. Situated in rows on the top surface of the microplate <b>400</b> and between the wells <b>412</b> are a plurality of elongated dielectric barrier members <b>402</b> similar to those described hereinabove. The inner electrodes <b>404</b> of the elongated dielectric barrier members <b>402</b> are electrically coupled to the AC voltage source through bus bars or contact planes <b>414</b> of the cassette <b>410</b>.

0054The elongated dielectric barrier members <b>402</b> are each spaced apart in this particular embodiment a pitch of about 4.5 mm. In alternative embodiments, where the well count is 96, the members <b>402</b> are spaced apart a pitch of about 9 mm. In yet another embodiment, where the wells <b>412</b> numbered 1536, the pitch is 2.25 mm. During a cleaning step, the wells <b>412</b> of the microplate <b>400</b> do not necessarily function as liquid holding devices. Rather, the wells <b>412</b> are used to allow receiving space for the probes when the probes are fully introduced between the elongated dielectric barrier members <b>402</b>.

0055In operation, the microplate <b>400</b> is placed in, for example, a deck mounted wash station. In, for example, an automated microplate liquid handling instrumentation, the system performs an assay test. Then, at least the probe tips of the fluid handling device would need a cleaning. As such, the fluid handling device enters the wash station. A set of automated commands initiate and control the probes to be introduced to the microplate <b>400</b> proximate the elongated dielectric barrier members <b>402</b>. At or about the same time, the AC voltage power source is initiated. Alternatively, the power source remains on during an extended period.

0056During the power-on phase, the probes are introduced to the dielectric members <b>402</b> of the microplate <b>400</b>. At that time, dielectric barrier discharges are formed between the members <b>402</b> and the probes (see, e.g., <figref idref="DRAWINGS">FIG. 2</figref>). In an embodiment where the probes are hollow, the reactive and energetic components or species of the plasma are repeatedly aspirated into the probes, using the fluid handling devices' aspirating and dispensing capabilities. The aspiration volume, rate and frequency are determined by the desired amount of cleaning/sterilization required.

0057Any volatized contaminants and other products from the plasma may be vented through the bottom of the microplate <b>400</b> by coupling the bottom of the tray <b>410</b> to a region of negative pressure such as a modest vacuum. This vacuum may be in communication with the wells <b>412</b> and is capable of drawing down plasma and reactive byproducts through to the bottom of the device and into an exhaust manifold (not shown) of the cleaning station test set up.

0058In an embodiment, ions, excited and metastables species (corresponding emitted photons), and free radicals are found in the atmospheric pressure plasma and remain long enough to remove substantially all of the impurities and contaminates from the previous test performed by the fluid handling device's probes. These particle species remain longer (see <figref idref="DRAWINGS">FIG. 5</figref>) than the initial plasma formed from a DBD or microdischarge and are therefore effective in cleaning the probes in preparation for a next test as the initially formed plasma itself.

0059In particular, <figref idref="DRAWINGS">FIG. 5</figref> represents a graph of the relative concentrations of different particle species in time after the initiation of a single microdischarge forming atmospheric pressure plasma in air. Metastables are represented by N₂(A) and N₂(B). Free radicals are represented by O₃, O(³P), N(⁴S) and NO. Free radicals and metastables are represented by O(¹D) and N(²D). In non-equilibrium microdischarges, the fast electrons created by the discharge mechanism mainly initiate the chemical reactions in the atmospheric pressure plasma. The fast electrons can inelastically collide with gas molecules and ionize, dissociate, and/or excite them to higher energy levels, thereby losing part of their energy, which is replenished by the electric field. The resulting ionic, free radical, and excited species can then, due to their high internal energies or reactivities, either dissociate or initiate other reactions.

0060In plasma chemistry, the transfer of energy, via electrons, to the species that take part in the reactions must be efficient. This can be accomplished by a very short discharge pulse. This is what occurs in a microdischarge. <figref idref="DRAWINGS">FIG. 5</figref> shows the evolution of the different particle species initiated by a single microdischarge in “air” (80% N₂, plus 20% O₂). The short current pulse of about 10 ns duration deposits energy in various excited levels of N₂and O₂, some of which lead to dissociation and finally to the formation of ozone and different nitrogen oxides. After about 50 ns, most charge carriers have disappeared and the chemical reactions proceed without major interference from charge carriers and additional gas heating.

0061<figref idref="DRAWINGS">FIG. 6</figref> is a top, partial perspective view of a plurality of probes being introduced to a plurality of elongated dielectric barrier members with coupled inner electrodes in accordance with another embodiment of the present invention. Referring to <figref idref="DRAWINGS">FIG. 6</figref>, there is provided a cleaning device <b>600</b>. The device <b>600</b> includes a plurality of elongated dielectric barrier members <b>602</b> arranged in a matrix or array, which lie in a plane. The members <b>602</b> are substantially regularly spaced apart from each other forming a gap <b>603</b> between adjacent members <b>602</b>. Each dielectric barrier member <b>602</b> includes an inner electrode <b>604</b> extending within, and substantially along the length of, respective elongated dielectric barrier members <b>602</b>. The inner electrodes <b>604</b> are electrically coupled to a voltage supply <b>608</b> similar to that described herein.

0062In addition, each dielectric barrier member <b>602</b> includes on its surface a secondary ground grid <b>609</b>. Here, the ground grid <b>609</b> is in the form of a conductive spiral, coupled to the surface of each dielectric barrier member <b>602</b> and to ground. In this manner, plasma will extend along the surface of each elongated dielectric barrier members <b>602</b> as designated by large arrows <b>610</b>. In this particular embodiment, conductive, electrically isolated, and non-conductive probes <b>606</b> can be treated by the plasma formed between spacing of the grid <b>609</b> because plasma formation is not necessarily dependent on the probe being conductive. Rather, plasma is formed independent of the probes on the surface of the members <b>602</b>.

0063A plurality of probes <b>606</b> are shown extending into open spaces or gaps <b>603</b> between the plurality of dielectric barrier members <b>602</b>. In one embodiment, the probes <b>606</b> are part of a fluid handling device. As such, the probes <b>606</b> are attached to and extend from a fluid handling device (not shown), which may be part of a microtiter plate test bed set up. In other embodiments, the probes <b>606</b> may be any form of an object that would benefit from plasma cleaning.

0064In the embodiment shown in <figref idref="DRAWINGS">FIG. 6</figref>, the elongated dielectric barrier members <b>602</b> are made of any type of material capable of providing a surface for a dielectric barrier discharge of atmospheric pressure plasma (described herein). Dielectric barrier material useful in this embodiment of the present invention includes, but is not limited to, ceramic, glass, plastic, polymer epoxy, or a composite of one or more such materials, such as fiberglass or a ceramic filled resin (available from Cotronics Corp., Wetherill Park, Australia). The various types of materials discussed with respect to previous figures apply here as well.

0065The inner electrode <b>604</b> may comprise any conductive material, including metals, alloys and conductive compounds as described herein with respect to the other figures. The inner electrodes <b>604</b> of the present invention may be formed using any method known in the art, including those mentioned herein in connection with the other figures.

0066In one use of this embodiment of the present invention, the secondary ground grid is conductive and made of formable conductive material described herein with respect to the inner electrode. For example, the ground grid can be a separate conductive wire or conductive paint deposited on the members, and the like, as described previously. The probes <b>606</b> are part of the fluid handling device and are introduced in the gap <b>603</b>, i.e., proximate the elongated dielectric barrier members <b>602</b> of the plasma cleaning device <b>600</b>. In this embodiment, the probe <b>606</b> can either conductive or non-conductive. If conductive, it is made of conductive material similar to that material described above in connection with the inner electrode <b>604</b>. In other embodiments, as described below, the probe is non-conductive and can be made of any non-conductive material known to one of ordinary skill in the art.

0067In addition to the above operation of introducing the probes <b>606</b> between the elongated dielectric barrier members <b>602</b>, similar to <figref idref="DRAWINGS">FIG. 1B</figref>, the probes <b>606</b> can be introduced proximate the elongated dielectric barrier members <b>602</b>. That is, each probe <b>606</b> may be introduced proximate one or more elongated dielectric barrier members <b>602</b>. When each probe <b>606</b> is introduced proximate two elongated dielectric barrier members <b>602</b>, the probe <b>606</b> may be introduced proximate or between the two elongated dielectric barrier members <b>602</b>.

0068<figref idref="DRAWINGS">FIG. 7</figref> is a top, partial perspective view of a plurality of probes <b>706</b> being introduced to a plurality of elongated dielectric barrier members <b>702</b> with coupled inner electrodes <b>704</b> in accordance with yet another embodiment of the present invention. Similar to <figref idref="DRAWINGS">FIG. 6</figref>, this embodiment includes a secondary ground plane <b>715</b>. In this embodiment, the ground plane <b>715</b> is in the form of a conductive mesh positioned either above or below the elongated dielectric barrier members <b>702</b>. <figref idref="DRAWINGS">FIG. 7</figref> depicts the ground plane <b>715</b> above the members for clarity purposes but it is to be understood that a ground plane below the members <b>702</b> is also contemplated by this embodiment of the present invention. In addition ground planes above and below are contemplated and within the scope of the present invention.

0069Similar to the earlier embodiments, this embodiment includes elongated dielectric barrier members, inner electrodes, probes and secondary ground grids as described hereinabove. In addition, although not shown, the inner electrodes are electrically coupled to a voltage source similar to that shown with respect to <figref idref="DRAWINGS">FIG. 6</figref> described. With the added conductive mesh secondary ground plane <b>715</b>, plasma will form between the ground plane portions <b>715</b> and the elongated dielectric barrier members <b>702</b>. Therefore, the probes <b>706</b> can be either conductive or non-conductive as herein described.

0070<figref idref="DRAWINGS">FIG. 8</figref> is a partial, cross sectional view of the embodiment shown in <figref idref="DRAWINGS">FIG. 7</figref>, depicting one example of the geometry and relationship among components of this embodiment of the present invention. The elongated dielectric barrier member <b>802</b> may comprise, for example, an elongated hollow tube with a hollow inner electrode <b>804</b> extended substantially the length of the elongated dielectric barrier member <b>802</b>. Alternatively, the elongated dielectric barrier member <b>802</b> may comprise other than a tube, such as a solid with a solid inner electrode <b>804</b>. The elongated dielectric barrier member <b>802</b> may be formed of different shapes as well. For example, and not in any way limiting, the shape of the elongated dielectric barrier member <b>802</b> may be tubular, circular, square, rectangular, oval, polygonal, triangular, trapezoidal, rhombus and irregular. If tubular, each elongated dielectric barrier member is about 2 mm in diameter and about 75 to about 120 mm long.

0071The elongated dielectric barrier members <b>802</b> are placed adjacent one another, defining a plane. The secondary ground plane <b>815</b> is shown on top of the elongated dielectric barrier members <b>802</b> but would be within the scope of this embodiment if they were below the members <b>802</b>. The members <b>802</b> are spaced at regular intervals and form a gap <b>803</b>, designated as spacing A. Alternatively, the members <b>802</b> can be staggered in a non-planar arrangement with respect to one another. The spacing A is sized to allow at least a portion of each of the plurality of probes <b>806</b> to be introduced proximate or between the elongated dielectric barrier members. The gap <b>803</b> or spacing A can approach zero, provided there is a sufficient gap to allow gas such as air to flow through the elongated dielectric barrier members <b>802</b>. Spacing A or gap <b>803</b> can range from about 0 mm to about 10 mm. The spacing A or gap <b>803</b> may also range from about 2 mm to about 9.5 mm. In one embodiment, the spacing A is about 9 mm. In another embodiment, the spacing A is about 4.5 mm. In yet another embodiment, the spacing A is about 2.25 mm. In addition, spacing C is provided. Spacing C is size to provide for the production of plasma between the ground plane <b>815</b> and the elongated dielectric barrier member <b>802</b> for a given applied voltage on inner electrodes <b>804</b>. Typically, spacing C ranges from about 0.0 mm to about 1 cm. It may also range from about 0.5 mm to about 2 mm.

0072<figref idref="DRAWINGS">FIG. 9</figref> is a top plan view of a matrix or array of a device including a ground plane similar to that shown in <figref idref="DRAWINGS">FIG. 7</figref>, depicting the plurality of elongated dielectric barrier members arranged in a microtiter plate format <b>900</b>. The microtiter plate format may be sized to accommodate about 96 openings for receiving a plurality of fluid handling probes. Alternatively, the microtiter plate is sized to accommodate about 384 openings for receiving a plurality of probes as depicted above. As an alternative, the wells and the pitch between rows of wells of the microtiter plate are sized to accommodate about 1536 openings for receiving a plurality of probes.

0073The microplate <b>900</b> has been equipped with an embodiment of the present invention having a ground plane or grid. Situated in rows on the top surface of the microplate <b>900</b> and between the wells <b>912</b> are a plurality of elongated dielectric barrier members <b>902</b> similar to those described hereinabove. The inner electrodes <b>904</b> of the elongated dielectric barrier members <b>902</b> are electrically coupled to the AC voltage source through bus bars or contact planes <b>914</b> of the cassette <b>910</b>. A meshed secondary ground plane <b>915</b> is disposed a spacing C from the elongated dielectric barrier members <b>902</b> on the top of the members. This secondary ground plane <b>915</b> is grounded with respect to the AC voltage source.

0074Similar to the microplate discussed herein, the elongated dielectric barrier members <b>902</b> are each spaced apart in this particular embodiment a pitch of about 4.5 mm. In alternative embodiments, where the well count is 96, the members <b>902</b> are spaced apart a pitch of about 9 mm. In yet another embodiment, where the wells <b>912</b> numbered 1536, the pitch is about 2.25 mm. The wells <b>912</b> are used to allow receiving space for the probes (not shown) when the probes are fully introduced between the elongated dielectric barrier members <b>902</b> and within the secondary ground grid <b>915</b>.

0075In operation, the microplate <b>900</b> is placed in, for example, a deck mounted wash station. In, for example, an automated microplate liquid handling instrumentation, the system performs an assay test. Then, at least the probe tips of the fluid handling device would need a cleaning. As such, the fluid handling device enters the wash station. A set of automated commands initiate and control the probes to be introduced to the microplate <b>900</b> proximate the elongated dielectric barrier members <b>902</b>. At or about the same time, the AC voltage power source is initiated. Alternatively, the power source remains on during an extended period.

0076During the power-on phase, the probes are introduced to the dielectric members <b>902</b> of the microplate <b>900</b>. At that time, dielectric barrier discharges are formed between the members <b>902</b> and the secondary ground plane <b>915</b>. In an embodiment where the probes are hollow, the reactive and energetic components or species of the plasma are repeatedly aspirated into the probes, using the fluid handling devices' aspirating and dispensing capabilities. The aspiration volume, rate and frequency are determined by the desired amount of cleaning/sterilization required.

0077Any volatized contaminants and other products from the plasma may be vented through the bottom of the microplate <b>900</b> by coupling the bottom of the tray <b>910</b> to a region of negative pressure such as a modest vacuum. This vacuum may be in communication with the wells <b>912</b> and is capable of drawing down plasma and reactive byproducts through to the bottom of the device and into an exhaust manifold (not shown) of the cleaning station test set up.

0078While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.